1. Field of the Invention
The present invention relates to an inductor for surface mounting used for a battery-driven electronic device or the like and a method for producing the same.
2. Description of the Related Art
FIG. 14 is a partially cut perspective view of a conventional inductor 50. FIG. 15 is an isometric view of a terminal 31 of the inductor 50. FIGS. 16A through 16E are isometric views illustrating a method for producing the inductor 50.
As shown in FIGS. 14 and 15, the terminal 31 is drawn outside from an intermediate level part of a side surface of a terminal table 30 (namely, an intermediate part of the side surface in the thickness direction); The terminal 31 is bent to be step-like. The terminal 31 includes a tip portion 31a, and the inductor 50 is mounted on an electronic device or the like in the state where a bottom surface of the tip portion 31a is in contact with a substrate of the electronic device or the like. The bottom surface of the tip portion 31a is on the same level as a bottom surface of the terminal table 30.
On a top surface of the terminal table 30, a drum-shaped core 28 is provided. The drum-shaped core 28 has a top flange 28b, a bottom flange 28c, and a central part 28a interposed between the top flange 28b and the bottom flange 28c and having a smaller diameter than the top and bottom flanges 28b and 28c. A wire 29 is wound around the central part 28a. Two ends 34 (only one is shown in FIG. 14) of the wire 29 are wound around a foot of the terminals 31 on the terminal table 30 and are treated by, for example, soldering for more secure electric connection to the terminals 31.
A cap-like core 27 covers the drum-shaped core 28, and is adhered to the terminal table 30 at contact surfaces thereof. The cap-like core 27 and the drum-shaped core 28 form a magnetic core of the inductor 50.
A method for producing an inductor 50 will be described with reference to FIGS. 16A through 16E.
As shown in FIG. 16A, a prescribed pattern is punched in a strip-like metal plate 33 by a pressing mold to form a lead frame 32 having guide holes 35 at prescribed positions and T-shaped terminal strips 31b extending inward from the lead frame 32. Next, the lead frame 32 is set in a resin molding apparatus (not shown). Then, insert molding is performed using a mold to form a terminal table 30 having the T-shaped terminal strips 31b inserted therethrough, as shown in FIG. 16B.
Next, the terminal strips 31b are cut to separate the terminal table 30 from the lead frame 32 as is shown in FIG. 16C. As shown in FIG. 16D, the terminal strips 31b are bent using a press mold to obtain step-like terminals 31.
Then, as shown in FIG. 16E, a drum-shaped core 28 is adhered on a top surface of the terminal table 30. A wire 29 is wound around a central part 28a of a drum-shaped shaped core. 28, and a cap-like core 27 (FIG. 14) is provided to cover the drum-shaped core 28 to form a magnetic core. Thus, the inductor 50 is completed.
As described above, the step-like terminals 31 of the conventional inductor 50 are formed by bending the T-shaped terminal strips 31b inserted through the terminal table 30. When the terminal strips 31b are bent, a mechanical stress is applied. Such a mechanical stress often causes generation of cracks in the terminal table 30, thereby lowering the mechanical strength of the terminals 31.
By bending the terminal strips 31b in this manner, the shape and the size of the terminals 31 are difficult to control with high precision. In the case where the terminals 31 do not have the shape and the size as designed, the inductor 50 including such terminals is not electrically connected to a printed circuit board in a satisfactory manner when the inductor 50 is mounted on a surface of the printed circuit board, resulting in defective mounting.
In the conventional inductor 50, two ends 34 of the wire 29 are wound around a foot of the terminals 31, which extend from the terminal table 30, and further soldered for more secure electric connection to the terminals 31. The winding process also provides a mechanical stress and thus can cause non-uniformity in the size of the terminals 31. Such difficulty in obtaining a satisfactorily precise size often causes defective mounting.
Moreover, in the conventional method for producing the inductor 50, after the terminal table 30 having the T-shaped terminal strips 31b inserted therethrough is formed by insert molding, the terminal strips 31b are cut to separate-the terminal table 30 from the lead frame 32. The terminal table 30 having the terminal strips 31b inserted therethrough, namely, an inductor in a half-completed state, is transported for further processing. During the transportation, the terminals 31 are exposed to mechanical stress, resulting in lower reliability and lower size precision of the terminals 31.